The present invention relates generally to transmission systems for transmitting force and motion in a mechanical system, and more particularly to mechanical interface devices for allowing humans to interface with computer systems.
Mechanical transmission systems are used in a variety of applications for various purposes. One type of application that uses mechanical transmission systems is human/computer interface devices. Such devices allow a user to input commands or other data to a computer system and thereby interact with an application program executing on the computer. One type of application program provides graphical environments with which users interact to perform a variety of interfacing activities, such as games or graphical simulations. In many types of games, a graphical environment is displayed on a display screen of the computer including one or more graphical representations of objects such as vehicles. For example, one popular type of game is a vehicle simulation game, where the player controls a vehicle such as an automobile, military tank, aircraft, space ship, etc. through a virtual environment. The graphical environment includes other objects and features with which the player's vehicle may interact, such as other vehicles, a side railing on a race track, a missile or other projectile, etc. Simulations are similar to such games except that the realism of the graphical environment and the interaction with such are typically more stressed since the simulation is used for training or learning purposes rather than entertainment. The interface device allows the user to control his or her vehicle in the environment, usually through physical motion in degrees of freedom provided by the interface device.
One popular interface device for use with vehicle simulations and games is a steering wheel controller. The controller simulates the steering wheel in an automobile or other vehicle and typically includes a wheel rotably coupled to a base support to provide a single rotary degree of freedom. As the player turns the wheel, a sensor relays a signal to a connected host computer which controls the display of the simulated vehicle under control and updates the graphical environment accordingly. In addition, other controls may also be provided such as buttons, dials, levers, etc. similar to such controls in a real vehicle in response to which the host computer similarly updates the graphical environment. The steering wheel controller includes sensors and in some cases a mechanical transmission system to convert the physical motion of the wheel rotation into electrical signals that indicate the position of the wheel to the host computer.
Force feedback steering wheel controllers and other interface devices are also known in the prior art. Force feedback provides the user with sensory "haptic" (feel) information about an simulated environment. Thus these devices typically include more elaborate mechanical transmission systems to convey the forces from actuators to the interface object manipulated by the user. For example, recently-available force feedback steering wheels for the home consumer market provide forces to the steering wheel and user by providing a motor coupled to the rotary shaft of the steering wheel. The host computer or other electronic controller can output control signals at appropriate times to provide forces on the steering wheel in conjunction with events in the graphical environment. For example, when the user's vehicle moves off the road onto a rough shoulder, forces can be output on the steering wheel to cause the wheel to jerk in random directions to simulate a bumpy feel and jolts caused by the rough surface. A collision into a railing on the road can cause a large jolt force on the steering wheel in a direction opposite to the direction of travel into the railing.
Force feedback interface devices, and other types of devices, typically use high fidelity mechanical transmission systems to transmit forces to the user object, i.e., transmission systems which transmit forces with little backlash, undesired play, and high bandwidth. Furthermore, the transmission system is often necessary to provide mechanical advantage to increase the magnitude of forces output by a motor, thus allowing smaller sized motors to be used as desired in home consumer interface devices. For example, currently-available force feedback steering wheel controllers use a transmission system to provide mechanical advantage to output the desired strength of forces; otherwise, a large motor must be used to provide the desired force magnitude, which can be expensive and bulky and thus is undesirable. In the prior art, transmission systems such as a pulley system provide the mechanical advantage, where, for example, one pulley is coupled to another through highly-tensioned belts. A large pulley ratio (gear ratio) is typically not desirable since too much friction is generated, leading to distortion of output forces. However, even if small pulley ratio is used, side loads on the steering wheel or other user object can be created by the highly-tensioned belts on the pulleys. These side loads may also distort forces unless high-quality bearings on the pulleys and other high-quality rotatable parts are used, which can greatly increase the expense of manufacturing the steering wheel controller. Such a result is not desirable in the competitive, low-cost consumer market. In other interface device embodiments, capstan drives are used, in which a cable rather than a belt is used between the pulley and drum. However, the capstan drive movement range of the prior art is limited, thus providing inherent limitations to the amount of mechanical advantage provided.